Portable electronic devices such as smartphones, tablets, notebooks and other electronic devices have become a necessity for communicating and interacting with others. The frequent use of portable electronic devices, however, uses a significant amount of power, which quickly depletes the batteries attached to these devices. Inductive charging pads and corresponding inductive coils in portable devices allow users to wirelessly charge a device by placing the device at a particular position on an inductive pad to allow for a contact-based charging of the device due to magnetic coupling between respective coils in the inductive pad and in the device.
Conventional inductive charging pads, however, suffer from many drawbacks. For one, users typically must place their devices at a specific position and in a certain orientation on the charging pad because gaps (“dead zones” or “cold zones”) exist on the surface of the charging pad. In other words, for optimal charging, the coil in the charging pad needs to be aligned with the coil in the device in order for the required magnetic coupling to occur. Additionally, placement of other metallic objects near an inductive charging pad may interfere with operation of the inductive charging pad, so even if the user places their device at the exact right position, if another metal object is also on the pad, then magnetic coupling still may not occur and the device will not be charged by the inductive charging pad. This results in a frustrating experience for many users as they may be unable to properly charge their devices. Also, inductive charging requires a relatively large receiver coil to be placed within a device to be charged, which is less than ideal for devices where internal space is at a premium.
Charging using electromagnetic radiation (e.g., microwave radiation waves) offers promise, but RF charging is typically focused on far-field charging and not near-field charging where the device to be charged is placed on top of the RF energy transmitter. Furthermore, controlling far-field gain is a challenge that also must be solved to avoid causing interference with other devices operating in certain frequency bands (e.g., microwave frequency bands).